U.S. patent number 6,262,718 [Application Number 08/357,626] was granted by the patent office on 2001-07-17 for touch-sensitive display apparatus.
This patent grant is currently assigned to International Business Machines Corporation. Invention is credited to Valerie McLaren Findlay, Andrew Knox.
United States Patent |
6,262,718 |
Findlay , et al. |
July 17, 2001 |
Touch-sensitive display apparatus
Abstract
A touch-sensitive display apparatus is disclosed, which includes
a display screen. A display drive means is connected to the display
screen for generating an image on the display screen in response to
an input video signal. A display processor is connected to the
display drive means for generating, in response to one or more
image control signals, at least one drive control signal for
configuring the display drive means to move the displayed image
relative to the display screen. Touch sensing means generates a
touch input signal in response to a tactile stimulus of the display
screen. The touch input signal is indicative of the location of the
tactile stimulus on the touch screen. A touch processor is
connected to the touch sensing means for converting, in dependence
on calibration data stored in a touch memory, the touch input
signal into coordinates defining the location of the tactile
stimulus on the display screen relative to features in the image
displayed on the display screen. The display processor includes
means for communicating correction data indicative of movement of
the displayed image relative to the display screen to the touch
processor. Touch processor comprises means for automatically
adjusting the calibration data stored in the touch memory to
re-align the coordinates generated by the touch processor to
features in the displayed image in response to the correction data
received from the display processor.
Inventors: |
Findlay; Valerie McLaren
(Glasgow, GB), Knox; Andrew (Kilbirnie,
GB) |
Assignee: |
International Business Machines
Corporation (Armonk, NY)
|
Family
ID: |
10749026 |
Appl.
No.: |
08/357,626 |
Filed: |
December 16, 1994 |
Foreign Application Priority Data
|
|
|
|
|
Jan 19, 1994 [GB] |
|
|
9400983 |
|
Current U.S.
Class: |
345/178;
345/173 |
Current CPC
Class: |
G06F
3/0418 (20130101) |
Current International
Class: |
G06F
3/033 (20060101); G09G 005/00 () |
Field of
Search: |
;345/173,174,175,178,179,180,182,156,157 ;178/18 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Saras; Steven
Attorney, Agent or Firm: Bracewell & Patterson, LLP
Claims
What is claimed is:
1. A touch-sensitive display apparatus comprising:
a display screen;
a display drive means connected to said display screen for
displaying an image within a display area of said display screen in
response to an input video signal;
a display processor connected to said display drive means for
generating, in response to one or more image control signals, at
least one drive control signal for configuring said display drive
means to adjust a parameter of said display area such that a
selected portion of said display area has a different position
relative to said display screen than said selected portion of said
display area had when said touch-sensitive display apparatus was
last calibrated;
a touch sensing means for generating a touch input signal in
response to a tactile stimulus of said display screen, said touch
input signal being indicative of a location of said tactile
stimulus on said display screen;
a touch processor connected to said touch sensing means for
converting, utilizing calibration data stored in a touch memory,
said touch input signal into coordinates defining said location of
said tactile stimulus on said display screen relative to features
in said image displayed within said display area of said display
screen;
wherein said display processor includes means for communicating
correction data to said touch processor indicative of said
different position of said selected portion of said display area
relative to said display screen, and said touch processor includes
means for automatically adjusting said calibration data stored in
said touch memory to re-align said coordinates generated by said
touch processor to features of said image in response to said
correction data received from said display processor.
2. The touch-sensitive display apparatus of claim 1, wherein said
touch sensing means comprises a touch sensitive screen mounted on
said display screen.
3. The touch-sensitive display apparatus of claim 1, and further
comprising a communication link connecting said touch processor to
said display processor.
4. The touch-sensitive display apparatus of claim 3, wherein said
communication link comprises a bus.
5. The touch-sensitive display apparatus of claim 1, wherein said
touch processor is integral to said display processor.
6. The touch-sensitive display apparatus of claim 1, wherein said
display screen comprises a cathode ray tube display screen.
7. The touch-sensitive display apparatus of claim 1, and further
comprising a user control connected to said display processor for
generating an image control signal in response to a manual
input.
8. The touch-sensitive display apparatus of claim 1, and further
comprising a system unit for generating said input video signal and
said image control signal and for receiving coordinates generated
by said touch processor.
9. A method for automatically maintaining the calibration of a
touch-sensitive display apparatus, said touch-sensitive display
apparatus including a memory, a display screen, and a touch sensing
means overlaying said display screen, said method comprising:
displaying a calibration target within a display area of said
display screen;
in response to a tactile stimulus of said touch sensing means,
calibrating said touch-sensitive display apparatus by storing
calibration data within said memory that correlates a location of
said tactile stimulus of said touch sensing means and coordinates
of said calibration target displayed within said display
screen;
thereafter, adjusting a parameter of said display area such that a
selected portion of said display area has a different position
relative to said display screen than said selected portion of said
display area had at said calibration; and
in response to said adjustment, automatically recalibrating said
touch-sensitive display apparatus by adjusting said calibration
data stored within said memory, wherein manual recalibration is
unnecessary following adjustment of display parameters.
10. The method for automatically maintaining calibration of a
touch-sensitive display apparatus of claim 9, wherein said step of
calibrating said touch-sensitive display apparatus comprises
storing coordinates of a selected corner of said display area
within said memory in association with said location of said
tactile stimulus of said touch sensing means.
11. The method for automatically maintaining calibration of a
touch-sensitive display apparatus of claim 10, wherein said step of
automatically recalibrating said touch-sensitive display apparatus
comprises updating said coordinates of said selected corner of said
display area within said memory.
12. The method for automatically maintaining calibration of a
touch-sensitive display apparatus of claims 9, wherein said step of
adjusting a parameter of said display area comprises varying a size
of said display area.
13. A touch-sensitive display apparatus, comprising:
a display screen;
a touch sensing means overlaying said display screen;
a processing unit coupled to said display screen, said processing
unit including:
a memory;
means for displaying a calibration target within a display area of
said display screen;
means, responsive to a tactile stimulus of said touch sensing
means, for calibrating said touch-sensitive display apparatus by
storing calibration data within said memory that correlates a
location of said tactile stimulus of said touch sensing means and
coordinates of said calibration target displayed within said
display screen;
means for thereafter adjusting a parameter of said display area
such that a selected portion of said display area has a different
position relative to said display screen than said selected portion
of said display area had at said calibration; and
means, responsive to said adjustment, for automatically
recalibrating said touch-sensitive display apparatus by adjusting
said calibration data stored within said memory, wherein manual
recalibration is unnecessary following adjustment of display
parameters.
14. The touch-sensitive display apparatus of claim 13, wherein said
means for calibrating said touch-sensitive display apparatus
comprises means for storing coordinates of a selected corner of
said display area within said memory in association with said
location of said tactile stimulus of said touch sensing means.
15. The touch-sensitive display apparatus of claim 14, wherein said
means for automatically recalibrating said touch-sensitive display
apparatus comprises means for updating said coordinates of said
selected corner of said display area within said memory.
16. The touch-sensitive display apparatus of claim 13, wherein said
means for adjusting a parameter of said display area comprises
means for varying a size of said display area.
Description
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates in general to a data processing
system, and in particular to touch-sensitive display apparatus for
inputting instructions to a data processing system in response to
tactile stimuli. Still more particularly, the present invention
relates to a touch-sensitive display apparatus which does not
require recalibration when image parameters are adjusted.
2. Description of the Related Art
Many raster-scanned display devices, such as cathode ray tube
displays and liquid crystal displays are now designed to be
compatible with a wide range of different computer systems each
capable of generating one or more different raster display formats
or "modes". Each mode is generally characterized by a different
pair of line and frame synchronization frequencies. Such display
devices usually have user controls which permit an operator to
correct geometric image distortions such as East-West pin-cushion
distortion or trapezoidal distortion. The user controls also permit
the operator to adjust parameters of the displayed image such as
width, height and position according to personal preference.
A typical touch sensitive display comprises a display device which
has a transparent touch screen mounted on its display screen. The
touch screen includes sensors for detecting a touch on the touch
screen by, for example, a stylus or an operator's finger. A touch
screen processor converts the outputs of the sensors into cartesian
coordinates indicative of the position of the touch on the screen.
The coordinates are communicated typically to a host computer
system to which the touch display is connected via a serial port
such as an RS232 port. The host computer system responds to the
input touch coordinates by moving a cursor on the display screen to
the position at which the touch was applied.
Conventionally, a calibration routine is performed to align the
coordinates produced by the touch screen processor with data
displayed on the screen. The calibration routine is typically in
the form of computer program microcode stored partly in a touch
memory of the touch display and partly in the host computer system
as device driver software. Typically, the host computer system
starts the calibration routine in response to an instruction from
the user. The host computer system, under control of the
calibration code in the device driver software, responds by
generating targets in the top left and bottom right corners of the
display area. The user is then instructed to touch the screen at
each of the targets in turn. The outputs generated by the sensors
in response to the touches are detected by the touch processor and
stored as digital reference values or calibration data in the touch
memory. The calibration microcode stored in the touch memory
instructs the touch processor to associate the reference values
stored in the touch memory with the top left and bottom right
corners of the display area. The touch processor, under the control
of the calibration microcode in the touch memory assigns top left
and bottom right coordinates of a field of sensitivity to the
reference values stored in the touch memory. The calibration
microcode stored in the touch memory then instructs the touch
processor to interpolate between the values stored in the touch
memory to assign intermediate values to a grid of coordinates
extending between the top left and bottom right coordinates of the
field of sensitivity. The touch processor effectively produces a
look up table for mapping digital values corresponding to outputs
from the sensors to coordinates within the field of sensitivity.
The coordinates of the field of sensitivity thus map directly to
the display area. On completion of the mapping, the touch processor
sends to message to the host computer system to indicate that the
calibration routine is complete. In response to the message, the
host computer system reverts to running normal application
software.
A problem with this arrangement is that if the displayed image is
moved relative to the field of sensitivity, the calibration data
stored in the touch memory is invalidated. Therefore, a touch to,
for example, an icon displayed in the displayed area may not invoke
the execution of the desired task by the host computer system. If
the mismatch is extreme, the coordinates received by the host
computer system may even invoke the unwanted execution of another
task. Therefore, in conventional touch displays, the calibration
routine must be repeated each time the image parameters are
adjusted. It should also be appreciated that, in conventional touch
displays, the calibration data may also be invalidated by a change
in display mode because the image may move from one display mode to
another.
Consequently, it would be desirable to provide a data processing
system having a touch screen which does not require recalibration
when image display parameters are modified.
SUMMARY OF THE INVENTION
It is therefore one object of the present invention to provide an
improved data processing system.
It is another object of the present invention to provide an
improved touch-sensitive display apparatus for inputting data to a
data processing system.
It is yet another object of the present invention to provide an
improved touch-sensitive display apparatus which does not require
recalibration in response to modification of image display
parameters.
The foregoing objects are achieved as is now described. A
touch-sensitive display apparatus is disclosed, which includes a
display screen. A display drive means is connected to the display
screen for generating an image on the display screen in response to
an input video signal. A display processor is connected to the
display drive means for generating, in response to one or more
image control signals, at least one drive control signal for
configuring the display drive means to move the displayed image
relative to the display screen. Touch sensing means generates a
touch input signal in response to a tactile stimulus of the display
screen. The touch input signal is indicative of the location of the
tactile stimulus on the touch screen. A touch processor is
connected to the touch sensing means for converting, in dependence
on calibration data stored in a touch memory, the touch input
signal into coordinates defining the location of the tactile
stimulus on the display screen relative to features in the image
displayed on the display screen. The display processor includes
means for communicating correction data indicative of movement of
the displayed image relative to the display screen to the touch
processor. Touch processor comprises means for automatically
adjusting the calibration data stored in the touch memory to
re-align the coordinates generated by the touch processor to
features in the displayed image in response to the correction data
received from the display processor.
The above as well as additional objectives, features, and
advantages of the present invention will become apparent in the
following detailed written description.
BRIEF DESCRIPTION OF THE DRAWINGS
The novel features believed characteristic of the invention are set
forth in the appended claims. The invention itself, however, as
well as a preferred mode of use, further objectives and advantages
thereof, will best be understood by reference to the following
detailed description of an illustrative embodiment when read in
conjunction with the accompanying drawings, wherein:
FIG. 1 is a block diagram of a preferred embodiment of the touch
sensitive display apparatus of the present invention;
FIG. 2 is a front view of the display screen of the display
apparatus showing the location of a basic set of calibration
points; and
FIG. 3 is a front view of the display screen of the display
apparatus showing the location of an enhanced set of calibration
points.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
Referring first to FIG. 1, a preferred embodiment of a touch
sensitive display apparatus utilizing the present invention
comprises a color cathode ray display tube (CRT) 10 connected to an
Extra High Tension (EHT) generator 30 and a video amplifier 60.
Line and frame deflection coils 80 and 70, respectively, are
disposed around the neck of the CRT 10. Deflection coils 80 and 70
are connected to line and frame scan circuits 40 and 50,
respectively. line scan circuit 40 and EHT generator 30 may each be
in the form of a fly back circuit, the operation of which is well
known by those skilled in the art. Furthermore, as is also
well-known in the art, EHT generator 30 and line scan circuit 40
may be integrated in a single flyback circuit. A power supply 20 is
connected via power supply rails V.sub.s and 0V to EHT generator
30, video amplifier 60, and line and frame scan circuits 40 and 50.
In use, power supply provides electrical power on supply rails
V.sub.s and 0V from Line and Neutral connections L and N to the
domestic electricity main supply 90. Power supply 20 may be in the
form of a switch mode power supply, the operation of which is
well-understood by those skilled in the art.
Power supply 20, EHT generator 40, video amplifier 60, and line and
frame scan circuits 40 and 50 are each connected via a digital to
analog (D to A) convertor 100 to outputs of a display processor
140. Display processor 140 comprises processor logic, preferably in
the form of a microprocessor. Display processor 140 is connected
via address and data buses to a display memory 150. A user control
panel 110 is connected to key-pad interrupt lines of display
processor 140. Control panel 110 comprises a plurality of manual
operable switches.
A touch sensitive screen 170 is provided on CRT 10. Touch screen
170 comprises sensors (not shown) for detecting a tactile stimulus
of the screen. Touch screen 170 may be implemented by conventional
techniques. For example, touch screen 170 may include a system of
strain gauges in bezel mountings of CRT 10. Alternatively, touch
screen 170 may indude a capacitive or surface acoustic wave overlay
on the screen of CRT 10. The output of the sensors of touch screen
170 are connected, via an analog to digital (A to D) convertor 130
to a touch processor 120. Touch processor 120 comprises processor
logic, preferably in the form of a microprocessor. Touch processor
120 is connected via address and data buses to a touch memory 160.
Touch processor 120 is also connectable to a host computer system
180 such as a personal computer via a communication link 240.
Communication link 240 may be a mouse interface or a serial link
such as an RS232 link.
In operation, EHT generator 30 generates an electric field within
CRT 10 for accelerating electrons in beams corresponding to the
primary colors of red, green and blue towards the screen of CRT 10.
Line and frame scan circuits 40 and 50 generate line and frame scan
currents in deflection coils 70 and 80. The line and frame scan
currents are in the form of ramp signals to produce time-varying
magnetic fields that scan the electron beams across the screen of
CRT 10 in a raster pattern. The line and frame scan signals are
synchronized by line and frame scan circuits 40 and 50 to input
line and frame synchronization (sync) signals (not shown)
generated, for example, by a host computer system 180 to which the
display apparatus is connected. Video amplifier 60 modulates the
red, green and blue electron beams to produce an output display on
CRT 10 as a function of corresponding red, green and blue input
video signals (not shown) also generated by the host computer
system 180.
Display processor 140 is configured by computer program microcode
stored in display memory 150 to control the outputs of EHT
generator 30, video amplifier 60, power supply 20 and line and
frame scan circuits 40 and 50 via D to A convertor 100 and control
links 190 to 230 as functions of display mode data stored in memory
150 and inputs from user control 110. The display mode data stored
in memory 150 includes sets of preset image parameter values each
corresponding to a different popular display mode such as, for
example, 1024.times.768 pixels, 640.times.480 pixels, or
1280.times.1024 pixels. Each set of image display parameter values
includes height and centering values for setting the output of
frame scan circuit 50 via control link 200, and width and centering
values for controlling line scan circuit 40 via control link 220.
In addition, memory 150 includes common preset image parameter
values for controlling the gain and cut-off of each of the red,
green and blue channels of video amplifier 60 via control link 230;
and preset control values for controlling the outputs of EHT
generator 30 and power supply 20 via control links 190 and 210. The
parameter values stored in memory 150 are selected by display
processor 140 under microcode control in response to input mode
information from host computer system 180. The mode information may
be provided to the display conventionally, for example, by coding
input line and frame sync signals generated by host computer system
180. Display processor 140 processes the selected image parameter
values to generate digital outputs to D to A convertor 100. D to A
convertor 100 converts the digital outputs from display processor
140 into analog control levels on control links 190-230.
A user may also manually adjust the digital values controlling red,
green and blue video gains and cutoffs at video amplifier 60; and
image width, height, and centering at line and frame scan circuit
40 and 50 via the user control panel 110. User control panel 110
includes a set of up/down control keys for each of image height,
centering, width, brightness and contrast. When, for example, the
width up key is depressed, user control panel 110 issues a
interrupt to display processor 140. The source of the interrupt is
determined by display processor 140 via an interrupt polling
routine in the controlling microcode. In response to the interrupt
from the width key, display processor progressively increases the
corresponding digital output at D to A convertor 100, thereby
increasing the corresponding analog level sent to line scan circuit
40 on control link 220. The width of the image progressively
increases. When the desired width is reached, the user releases the
key. The removal of the interrupt is detected by display processor
110, and the digital value setting the width control level on
control link 220 is retained. The height, centering, brightness and
contrast setting can be adjusted by the user in similar fashion.
User control panel 110 further includes a store key. When the user
depresses the store key, an interrupt is produced to which display
processor 140 responds by storing in memory 150 parameter values
corresponding the current settings of the digital outputs to D to A
convertor 100. The user can thus program into the display device
specific display image parameters according to personal
preference.
When a user touches touch screen 170 with a finger or stylus, the
sensors of touch screen 170 generate analog signals indicative of
the location and force of the touch. The analog signals are
converted to digital values by A to D convertor 130. Touch
processor 120 is configured by microcode stored in touch memory 160
to translate the positional digital values received from A to D
convertor 130 into cartesian (X,Y) coordinate data as a function of
calibration data also stored in the touch memory. The calibration
data effectively subdivides the touch screen into a grid of
coordinate points. The coordinate data is transmitted by touch
processor 120 to host computer system 180 via communication link
240. Communication link 240 may be a serial communication link such
as an RS232 communication link or the like.
To calibrate touch screen 170 after, for example, power on, a
calibration routine may be executed to determine the calibration
data for storage in touch memory 160. The calibration routine is in
the form of computer program microcode stored partly in touch
memory 160 and partly in host computer system 180 as device driver
software. When the touch display is turned on, touch processor 120,
under control of the calibration microcode stored in touch memory
160, sends a command to host computer system 180 via link 240
requesting that host computer system 180 start the calibration
routine.
Referring now to FIG. 2, host computer system 180, under control of
the calibration code in the device driver software, responds to the
request from touch processor 120 by generating targets 260 and 270
in the top left and bottom right corners of the display area on the
screen of CRT 10. The user is instructed to touch the screen at
each of the targets 260 and 270 in turn. The analog outputs
generated by the sensors of touch screen 170 in response to the
touches are converted to digital values by A to D convertor 130.
The digital values are detected by touch processor 120 and stored
as calibration data in touch memory 160. The calibration microcode
stored in touch memory 160 instructs touch processor 120 to
associate the reference values stored in touch memory 160 with the
top left and bottom right corners of the display area. Touch
processor 120, under the control of the calibration microcode in
touch memory 160 assigns top left and bottom right coordinates of a
field of sensitivity to the reference values stored in touch memory
160. The calibration microcode stored in touch memory 160 then
instructs touch processor 120 to interpolate between the values
stored in touch memory 160 to assign intermediate values to a grid
of coordinates extending between the top left and bottom right
coordinates of the field of sensitivity. Touch processor 120
effectively produces a look-up table for mapping digital values
corresponding to outputs from the sensors of touch screen 170 to
coordinates within the field of sensitivity. The coordinates of the
field of sensitivity thus map directly to the display area on the
screen of CRT 10. On completion of the mapping, touch processor 120
sends a message to host computer system 180 to indicate that the
calibration routine is complete. In response to the message, host
computer system 180 reverts to running normal application
software.
In accordance with the present invention, touch processor 120 is
connected to display processor 140 via a communication bus 250 such
as an I.sup.2 C bus or the like. In operation, if the image height,
width or centering setting stored in display memory 150 are
changed, either by manual adjustment via user control 110 or by a
change in display mode issued by host computer system 180, display
processor 140 is configured by microcode stored in display memory
150 to communicate change data indicative of the magnitude of the
change in image parameters to touch processor 120 via bus 250.
Touch processor 120, under the control of microcode stored in touch
memory 160, responds to the change data received from display
processor 140 by adjusting the calibration data stored in touch
memory 160 to re-align the field of sensitivity of touch screen 170
with the new dimensions and/or positioning of the displayed image.
Thus, touch sensitive display apparatus of the present invention
does not have to be recalibrated each time the display mode is
changed or the dimensions and/or positioning of the image is
required. The apparatus of the present invention can be calibrated
once upon initial power on, and thereafter it automatically
compensates for image movement produced by a mode change or by
manual adjustment of the displayed image.
What follows is a description of an algorithm for adjusting the
horizontal axis calibration data stored in touch memory 160 in
accordance with the present invention. For the purpose of the
description, assume:
i) CRT 10 is a so-called 14-inch CRT having a normal image width of
250 mm;
ii) D to A convertor 100 and display processor 140 in combination
provide a range of width extending from 215 mm to 279 mm; and
iii) D to A convertor 100 provides 6 bit D to A conversion.
D to A convertor 100 therefore has 64 possible output states. Thus,
a 1 mm change in image width corresponds to a Least Significant Bit
change in the output of D to A convertor 100. The image width
varies symmetrically about an imaginary line passing vertically
through the centers of the displayed image. Thus, a 1 mm increase
in width corresponds to the left and right edges of the displayed
image each moving by 0.5 mm relative to the screen of CRT 10.
Values indicating that the minimum image width is 215 mm and that
the Least Significant Bit of input data to D to A convertor 100
corresponds to a width change of 1 mm are preprogrammed in touch
memory 160 during manufacture. The image width can therefore be
defined as
Where DAC_VAL is the digital input to D to A convertor 100.
In accordance with the algorithm, when the user increases the image
width by 1 mm, display processor 140 sends the new DAC_VAL to touch
processor 120. On receipt of the new DAC_VAL, touch processor 120
adjusts the horizontal axis calibration data by 0.5 mm on either
side of the center of the field of sensitivity. For example, if the
origin of the field of sensitivity of touch screen 170 is central
(i.e., the horizontal and vertical axes of the coordinates produced
by touch processor 120 intersect at the center of the field of
sensitivity), touch processor 120 subtracts a value representing
0.5 mm to the left side reference value and adds a value
representing 0.5 mm to the right side reference value.
In another algorithm for adjusting the horizontal axis calibration
data in accordance with the present invention, touch memory 160 is
processor is preprogrammed during manufacture with the available
range of image width from the minimum to the maximum settings of
the input to D to A convertor 100. In accordance with the
algorithm, to initially calibrate the apparatus, the left and right
reference values are stored in touch memory 160 for the particular
input to D to A convertor 100 at the time. Subsequently, the
algorithm adjusts the left and right reference values in response
to a change in image width (i.e., a change in the input of D to A
convertor 100) according to the following equations: ##EQU1##
Where LEFT_CAL.sub.new is the new reference value defining the left
edge of the displayed image; LEFT_CAL.sub.old is the old reference
value defining the left edge of the image; DAC_VAL.sub.new is the
new input to D to A convertor 100 defining the new image width;
DAC_VAL.sub.old is the old input to D to A convertor 100 defining
the old image width; RIGHT_CAL.sub.new is the new reference value
defining the right edge of the displayed image; and
RIGHT_CAL.sub.old is the old reference value defining the right
edge of the displayed image.
It will be appreciated that similar algorithms can be used to
adjust the vertical axes reference values stored in touch memory
160 following, for example, an adjustment of the height of the
display image by the user. Algorithms for adjusting the vertical
and horizontal axes reference values following adjustment of the
centering of the displayed image will also be apparent.
In the embodiment of the present invention hereinbefore described,
because only the top left and bottom right corners of the displayed
image are used by the calibration routine, the field of sensitivity
of touch screen 170 can only be maintained in alignment with the
image displayed on CRT 10 provided that the displayed image remains
rectangular. In other words, only changes in image height, width
and centering can be compensated for. Referring now to FIG. 3, in a
modification of the embodiment hereinbefore described, host
computer system 180, under the control of the calibration routine
microcode generates 8 targets 260-330 in the display area on the
screen of CRT 10. Targets 260-290 are located in the four corners
of the display area. Targets 300-330 are located at the centers of
the four vertices of the display area. In operation, each of the
targets is used to produce reference values which are stored in
touch memory 180 in accordance with the process hereinbefore
described. However, it will be appreciated that the additional
reference values corresponding to targets 280-330 permit the touch
display to compensate for additional image movements. For example,
targets 260-300 and 320 permit the touch display to compensate for
East-West pin-cushion or trapezoidal distortions in addition to
changes in height, width and centering. Targets 310 and 330 permit
the touch display to compensate for North-South pin-cushion or
trapezoidal distortions.
In the embodiments of the present invention hereinbefore described,
the calibration data for touch screen 170 is stored in touch memory
160. It will be appreciated, however, that in other embodiments of
the present invention, the calibration data may be stored in a
memory of host computer system 180 and updated via bus 250, touch
processor 120 and serial communication link 240. Furthermore, in
the preferred embodiment of the present invention hereinbefore
described, the touch-sensitive display apparatus comprises a touch
processor 120 and a separate display processor 140. However, it
will be appreciated that, in other embodiments of the present
invention, the functions of both touch processor 120 and display
processor 140 may be performed by a single processor device in
which the function of updating calibration data for touch screen
170 provided by bus 250 is emulated by computer program microcode
controlling the single processor.
Preferred embodiments of the present invention have been
hereinbefore described with reference to touch-sensitive display
apparatus based on a color CRT. However, it will be appreciated
that the present invention is equally applicable to touch-sensitive
display apparatus having different types of display screen such as,
for example, monochrome CRTs or LCD panels of either color or
monochrome form. In the embodiments of the present invention
hereinbefore described, tactile stimulus was detected by touch
sensing means in the form of touch sensitive screen 170. However,
it will be appreciated that the present invention is equally
applicable to touch sensitive display apparatus having other forms
of touch sensing means. For example, the present invention is
equally applicable to touch sensitive display apparatus in which
the touch sensing means comprises a plinth for supporting a
conventional display device. Tactile stimuli of the display screen
are transferred to the plinth through the display device. Strain
gauges located in the plinth convert the forces exerted on the
plinth by the touch stimuli of the display screen into electrical
signals indicative of the location of the touch stimuli on the
display screen. By way of another example, the present invention is
equally applicable to touch sensitive display apparatus in which
the touch means comprises an optical system for detecting tactile
stimuli of the display screen. The optical system may, for example,
comprise a light beam which is scanned across the screen and
photo-detector for detecting the location of a tactile stimulus
through a corresponding interruption of the passage of the scanned
light beam. Alternatively, the optical system may comprise arrays
of light sources and photo-detectors mounted on opposite sides of
the display screen for detecting the location of a tactile stimulus
through an interruption of the passage of light between a
corresponding light source/photo-detector pair.
While the invention has been particularly shown and described with
reference to a preferred embodiment, it will be understood by those
skilled in the art that various changes in form and detail may be
made therein without departing from the spirit and scope of the
invention.
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